Abstract: Hydrodynamics of fluid and particles were simulated using a low density ratio-based kinetic theory of granular flow (KTGF) in subcritical water (SbW) fluidized beds (FB). Results indicated that the fluidization state of the SbW-particles mixture changes progressively from particulate to aggregative, indicating that a transitional state exists between aggregative and particulate fluidization. Wavy-like and churn-like flows were found along bed height in SbW FBs, unlike the homogeneous fluidization found in atmospheric water (AW) FBs and wispy-annular-like flow found in supercritical water (SCW) FBs. The predicted axial velocities and RMS fluctuating velocities of particles agreed approximately with measurements reported in the literature. The effect of fluid pressure and temperature, inlet fluid velocity and particle density on distributions of solid volume fractions and velocities were analyzed in SbW FBs.